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Author Topic:   AC-operated Charger for Montauk with ACR
Nauti Tauk posted 08-21-2010 08:16 AM ET (US)   Profile for Nauti Tauk   Send Email to Nauti Tauk  
I would like to add an [AC-operated] onboard battery charger to our 170 Montauk. I have installed the Blue Sea Systems automatic combiner relay (ACR) and battery switch to help keep the trolling motor battery charged while underway. The charger installation will add convenience by keeping both the starting and trolling batteries fully charged while on the trailer. Will a MinnKota MK210 two bank charger interfere with the operation of the charging relay? Blue Sea Systems recommended using a charger on the starting battery only. The relay would see the trolling battery when the starting battery was fully charged and bring the trolling battery up to full charge. This setup is fine except it doesn't take into account a faulty cell, weak cell, or other malfunction of the starting battery which would not allow that battery to come up to full charge, thus keeping the ACR from charging the trolling battery. I am not familiar with all the technical aspects of batteries, relays, loading, thresholds, voltage drops, trigger levels, etc.,so I'm asking for help. Both batteries are combination starting and deep-cycle Series-27 wet cell. One is brand new NAPA; the other a three-year-old Wally World.
jimh posted 08-21-2010 08:36 AM ET (US)     Profile for jimh  Send Email to jimh     
If you have the Blue Sea Systems ACR with the starting isolation feature, you could use that circuit to suppress the ACR from closing when your dual-battery AC-operated charger is in use. To make this feature automatic, add a new relay with a 120-VAC coil. Wire the coil of this new relay in parallel with the 120-VAC feed to the battery charger. Whenever there is power to the battery charger, the relay will operate. Wire a new circuit from the starting battery, through the normally-open contacts of the new relay, to the starting isolation circuit of the ACR. In this way, whenever the AC-operated battery charger is in use, the ACR will be supplied with 12-volts from the battery to its starting isolation terminal, causing the ACR to not close.

To prevent this circuit from back-feeding 12-volts to the ignition starting circuit, you must include two steering diodes or isolation diodes, so that current can only flow into the starting isolation circuit from the new relay, and cannot flow back into the starting circuit of the ignition key.

Or, follow the directions from Blue Sea Systems and use a single-bank charger. If you have a shorted cell in your starting battery you will not be operating the boat for very long in that condition. You would not want to try to charge the starting battery with a shorted cell from the AC-operated charger for very long. Also, the battery with the shorted cell would tend to hog all the charging current from the typical two-battery charger, anyways, so there is not much benefit from being able to do this.

jimh posted 08-21-2010 08:56 AM ET (US)     Profile for jimh  Send Email to jimh     
Revised idea:

Even simpler, on the new relay get a Form-C contact or SPDT arrangement. Connect the starting isolation circuit from the ACR to the COM of the relay. Connect the feed from the ignition switch to the NORMALLY CLOSED contact. Connect the feed from the battery to the NORMALLY OPEN contact. In this way the starting isolation circuit works as originally intended when the battery charger is not in use. When the battery charger is in use, the new relay moves the feed to the starting isolation circuit on the ACR over to the 12-volts from the battery, suppressing the ACR from closing.

DeeVee posted 08-21-2010 11:35 AM ET (US)     Profile for DeeVee  Send Email to DeeVee     

Jimh's two suggestions sound a little more complicated than the system installed on my Outrage 22.

I used the BEP Marine 3 switch/automatic charging relay cluster, wired per their instructions. This switch arrangement isolates the starting battery from the house battery, charging the starting battery, then the house battery, in that order. The two batteries can be connected together with the 3rd switch in case of emergency.

I then installed a 2 bank charger, wired per their instructions. When parked in the carport on the trailer, all the battery switches are in the off position, and the charger is plugged in.

Maybe ignorance is bliss, but this arrangement has worked flawlessly for me for the past 3 years.

Doug Vazquez

Nauti Tauk posted 08-21-2010 02:21 PM ET (US)     Profile for Nauti Tauk  Send Email to Nauti Tauk     
One of the joys of owning a Montauk is simplicity. Guess I'll just keep it simple and use an onboard single bank charger.
jimh posted 08-21-2010 05:30 PM ET (US)     Profile for jimh  Send Email to jimh     
If the ACR is wired on the LOAD side of the ON-OFF switches, then when the switch is in the OFF position, the ACR stops working. Then, as long as you always ran the AC-operated charger when the battery switch was in the OFF position, the ACR relay would never affect the battery charging.
jimh posted 08-25-2010 08:57 AM ET (US)     Profile for jimh  Send Email to jimh     
Via email I received this pointer to the discussion on the Blue Sea Systems website in which they elaborate on the reasoning used to recommend against use of their ACR with multi-bank battery chargers:

That article explains the concern quite well, however, I think in most cases there is little to worry about. Th concern expressed by Blue Sea Systems is for very smart or specialized battery chargers which employ intelligent charging algorithms to vary the charging current to the attached battery so as to optimize the chemistry of the battery in the re-charge cycle. This type of sophistication is employed in some marine battery chargers. Blue Sea Systems also assumes that if a dual bank charger is used, and if the charger is of this highly sophisticated design, that each bank of the charger will be operating completely independently of the other. Further, Blue Sea Systems also assume that it might be possible in a multi-bank charger for one bank to be configured for a standard lead-acid battery while another bank was configured for a gel-cell battery. Thus, if you have a sophisticated battery charger with varying charge cycle algorithms, have a multi-bank charger where each bank operates completely independently of the other banks, and have a charger which allows each bank to be set for a particular battery type to optimize the charging voltage, then there is reasonable concern for the action of an ACR putting two batteries in parallel while being charged by such a charger. However, if you have a simple battery charger with dual outputs, I wouldn't worry about the ACR putting the batteries in parallel.

jimh posted 08-25-2010 09:01 AM ET (US)     Profile for jimh  Send Email to jimh     
Blue Sea Systems also used the same idea I presented above: use an AC-operated relay to disable the operation of ACR when the battery charger is in use. Blue Sea Systems offers a simpler technique than I proposed: they use a relay to open the negative connection from the ACR to the battery system negative bus. This also stops the ACR from closing.

Blue Sea Systems suggests using a OMRON relay of the type G48. I believe this is a typographic error. OMRON has no relay type G48. However, OMRON does have a relay type G4B. Unfortunately, the G4B series relays are discontinued.

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